Is Your Home Protected from Earthquake Disaster? A Homeowner’s Guide to Earthquake Retrofit

Is Your
Is Y
Home
Protected
From
Earthq
Ear
uak
thq
e
uak
Disaster?
A Homeowner’s Guide
to Earthquake Retrofit

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Prepared by the Institute for Business & Home Safety. The Institute for Business & Home Safety (IBHS) is
an initiative of the insurance industry to reduce deaths, injuries, property damage, economic losses and human
suffering caused by natural disasters. IBHS is a nonprofit research and communications organization com-
mitted to institutionalizing natural disaster protection as a public value.
acknowledgments
The staff of the Institute for Business & Home Safety (IBHS) wishes to acknowledge the valuable input of all
those involved in preparing this brochure. In particular, we extend our thanks to:
The IBHS Earthquake Peril Committee Members
The IBHS Public Relations Committee Members
The IBHS Retrofit Committee Members
The National Geophysical Data Center (NGDC)
Earthquake Engineering Research Center, University of California, Berkeley (EERC, UCB)
Earthquake Engineering Research Institute (EERI)
cover photo credits
EERI Northridge Earthquake Reconnaissance Team, J. Hall, CIT; F. Desler, APA; Godden Collection,
EERC, UCB; and USGS, D. Perkins
architectural illustrations
W. Spaulding, AIA
disclaimer
The suggestions and recommendations you will read in this guide are based on professional judgment, expe-
rience and research. The authors, contributors and publisher disclaim all warranties and guarantees with
respect to the information in the document and assume no liability or responsibility with respect to the infor-
mation.
(c) 1999 Institute for Business & Home Safety
All rights reserved.
ISBN 1-885312-22-9
A Homeowner’s Guide to Earthquake Retrofit

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table of contents
introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
earthquakes and your home . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2
Earthquakes: What, When, Where and Why . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2
Measuring an Earthquake’s Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
What You Feel and Why You Feel It . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
What Your Home Experiences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
What You Can Do . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
nonstructural retrofits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
Bookcases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
Cabinets and Drawers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
Picture Frames and Bulletin Boards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
Ceiling Lights, Suspended Ceilings and Hanging Fixtures . . . . . . . . . . . . . . . . . .13
Windows and Doors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
Large Appliances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
Water Heaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
structural retrofits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
Foundation Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
Slab-on-Grade Foundations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
Crawl Space and Basement Foundations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
Post-and-pier Foundations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
Floor Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
Wall Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
Wood-Framed Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
Unreinforced Masonry Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29
Roof Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30
Unreinforced Chimneys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
Garages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33
Room Additions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33
home improvement project list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34
before, during and after: be completely prepared . . . . . . . . . . . . . . . . . . . . . .35
references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37
additional sources of information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38
ibhs member companies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41
checklist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42
table of contents

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F. Desler, APA
Top: Earthquake dam-
age in Kobe, Japan.
Right: San Francisco
Marina fire caused by
broken gas lines.
Background: Shored
building in the Marina
District, San Francisco.
USGS, D. Perkins
EERI, J. Egan
A Homeowner’s Guide to Earthquake Retrofit

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introduction
arthquakes occur suddenly with
• key areas of your home that are
little or no warning, during any
especially susceptible to damage;
Eseason and at any time of day. •ways you can reduce damage to
Although the West Coast generally has
your home and belongings; and,
the greatest earthquake activity, the po-
• what you can do to protect yourself
tential for earthquakes exists in almost
and your family.
every corner of the United States.
The information and suggestions pre-
More than 3,360 Americans have died
sented in this brochure range from
during earthquakes in the last century,
simple weekend tasks that require
and homes in all 50 states have suf-
basic carpentry skills to involved pro-
fered damage in the last 250 years.1
jects that may require professional
So, what can you do to protect your-
assistance. Before starting on any
self, your home and its contents from
activity, make sure you are comfort-
earthquakes? This brochure will help
able with the required skill level. If
you by providing information about:
you are uncertain, contact a profes-
• the relationship between your home
sional engineer, architect or building
and an earthquake;
contractor.
Damage in
San Francisco’s
Marina District.
J. Preli
1Based on U.S. Geological Survey numbers.
1
introduction

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earthquakes and
your home
Earthquakes: What,
Eventually, the fault reaches a breaking
When, Where and Why
point and slips suddenly, sometimes by
AA/NGDC
yards or sometimes only by inches.
Did you know that the ground
This sudden vertical or lateral (side-
NO
beneath you is constantly moving? The
ways) movement releases seismic
Earth’s surface is broken into many dif-
waves, which we feel as an earthquake.
ferent plates, which float on top of the
The point where the fault first slips is
Earth’s quasi-liquid mantle. Typically,
located deep within the earth and is
one plate interacts with another by
called the hypocenter. Directly above
either colliding with it, sliding past it
that, on the earth’s surface, is the epi-
or pushing itself underneath it. These
center. Figure 1 highlights the key ele-
areas along which plates interact are
ments of an earthquake.
known as geological faults.
In the United States, the most active
As plates move over time, the edge of
faults are along the West Coast—the
one plate often catches itself on anoth-
most famous being the San Andreas
er, forcing that portion of the fault to
Fault system that runs through the
remain motionless while stress builds.
state of California. This fault system
AA/NGDC
NO
Top: The San
Figure 1: Key Elements of an Earthquake
Andreas Fault in
the Carrizo Plain
Fault-line
area, Calif.
Bottom: The fault
scarp of the
Landers earth-
quake, Calif.
Epicenter
Plate
Plate
Hypocenter
Fault-plane
2
A Homeowner’s Guide to Earthquake Retrofit

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separates the North American Plate from
the Pacific Plate. Despite the large number
of earthquakes associated with this and
other plate boundaries, earthquakes are not
restricted to just the plate edges. Approx-
imately five percent of earthquakes occur
within the central part of a plate. These
earthquakes are known as intraplate earth-
Number of Events: 7,667
quakes, and have occurred in recent history
Data provided by the National Geophysical Data Center
in Charleston, South Carolina, and the
Mississippi Valley near New Madrid,
Missouri.
Remember, even if you don’t live in one of
these areas, you are still at risk. The maps
presented in Figure 2 show where earth-
quakes have been recorded in the past hun-
dred years. As you can see, no place is truly
safe from earthquakes.
Figure 2: Alaskan, Hawaiian
and Mainland Earthquakes
Number of Events: 1,507
Data provided by the National Geophysical Data Center
Number of Events: >14,000
Data provided by the National Geophysical Data Center
3
earthquakes and your home

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Measuring an
Earthquake’s Size
Seismologists estimate the size, or magni-
t
o
v
er
tude, of an earthquake in several different
ways. The Richter scale measures the size
, C. S
of the earthquake’s waves (amplitude);
r
v
ey
u
whereas, the moment magnitude scale
estimates the total energy released during
the slip of a fault. Because the moment
eological S
magnitude scale is more objective than
the Richter scale, it is now more com-
U.S. G
monly used. Figure 3 shows different
levels of earthquakes and their corre-
sponding moment magnitudes (Mw).
Fissure in
What You Feel
Santa Cruz
and Why You Feel It
Mountains, Calif.
The amount of movement you experi-
Figure 3: Moment Magnitude Scale
ence during an earthquake doesn’t
depend just upon its magnitude. Where
you’re located in relation to the earth-
quake’s epicenter also has an effect. The
farther away you are, the less shaking you
feel, since the seismic waves lose energy
as they travel through the earth. Imagine
a drop of water hitting the surface of a
pond. As the circular waves travel away
from the impact, they lose energy and
reduce in size and frequency. In time,
they disappear altogether.
Also, the kind of soil underneath and
around you plays a large role in how
much of the earthquake you experience.
Unlike water, soil is not uniform through-
Short History of U.S. Earthquakes:
(Moment Magnitude Scale—MW)
1755
Cape Anne, MA
~6.0 Mw
1812
New Madrid, MO
~7.8 Mw
1886
Charleston, SC
~7.0 Mw
1906
San Francisco, CA
~7.7 Mw
1944 Massena,
NY
~5.5 Mw
1964
Alaska
9.2 Mw
Turnagain Heights
1989
Loma Prieta, CA
7.0 Mw
Landslide;
1994
Northridge, CA
6.7 Mw
AA/NGDC
Anchorage, Alaska.
NO
4
A Homeowner’s Guide to Earthquake Retrofit

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Figure 4: Your Home in an Earthquake
out. The soil type can have a dramatic effect on
the way seismic waves travel through the earth.
Home at Rest;
For instance softer, less compact soil can actual-
Ground at Rest
ly increase the forces. More stable soils, such as
bedrock or compacted fill, dissipate an earth-
quake’s energy more quickly.
Leftward
Movement
Three major factors – an earthquake’s magni-
Begins
tude, your proximity to the epicenter and the
condition of the soil around you – determine
the amount of shaking you feel. The Modified
Mercalli Intensity scale measures this intensity
by evaluating the earthquake’s effect on you
Rightward
and your home.
Movement
Begins
What Your Home
Ground Comes
Experiences
to Rest
Imagine that a strong earthquake strikes where
you live. Loose items fall and break. Cabinets
and bookcases tip over, blocking exits. Dust bil-
Ground
lows everywhere. Gas and water lines break,
at Rest;
and phone and electrical service are interrupted
Home
for days. Your home may collapse, slide off its
Continues
to Move
foundation or simply come apart at the seams.
Due to
Inertia
Figure 4 illustrates how your home reacts in an
earthquake. Because it is not able to move in sync
with the surrounding ground, your home and its
contents can experience substantial damage.
gan
eagor
USGS. R
EERI, J. E
A sand boil near El Centro, Calif.
Building collapse in Marina
provides evidence of an earthquake.
District, San Francisco, Calif.
5
earthquakes and your home

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What You Can Do
You can protect your home by modifying it,
or retrofitting it, in two different ways:
Nonstructural retrofits protect your home’s
contents against damage with little cost and
effort. Examples of retrofits include:
• securing water heaters, large appliances,
t
o
v
er
bookcases, pictures and bulletin boards;
• latching cabinet doors; and
• using safety film on windows.
USGS, C. S
To complete these improvements simply
follow the instructions in this brochure. In
most cases, you won’t need a building per-
mit. It’s a good idea, however, to contact
your local building department to make
sure.
Structural retrofits strengthen your home’s
structure or skeleton so it can better with-
stand the force of an earthquake. Your
home’s structure is made up of many differ-
ent parts, or components, which must work
AA/NGDC
together in order to resist an earthquake.
NO
Modifications to your home’s structure tend
Top: Structure shifted
to be quite involved and generally require
on its foundation in
the expertise of a registered design profes-
Watsonville, Calif.
sional (engineer, architect or building con-
Bottom: Nonstruc-
tractor) and your local building depart-
tural kitchen damage,
ment’s approval. Use this brochure to iden-
Northridge, Calif.
tify potential problem areas in your own
home. If you have any questions or con-
cerns about what you see, contact a profes-
sional engineer or architect.
6
A Homeowner’s Guide to Earthquake Retrofit

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